Method for artificial synthesis of diamonds



July 28, 1964 J. A. BRINKMAN ETAL 3,142,539

METHOD FOR ARTIFICIAL SYNTHESIS OF DIAMQNDS Filed July 1, 1960Sheets-Sheet 1 P RESSURE REGULATOR BALLAST INVENTORS J A. BRINKIAN FIG.I C LES J. IEECHAN PERM I. DIEOKANP sywiw ATTORNE July 28, 1964 J. A.BRINKMAN ETAL 3,142,539

METHOD FOR ARTIFICIAL SYNTHESIS OF DIAMONDS Filed July 1, 1960 5Sheets-Sheet 2 FIG.

GROWTH RATE July 28, 1964 J. A. BRINKMAN ETAL 3,142,539

METHOD FOR ARTIFICIAL SYNTHESIS OF DIAMONDS Filed July 1, 1960 5Sheets-Sheet 3 NVENTORS JOHN A. mum

H R E AN 6 A L MEEGHAN BY HERMAN M. DIEOKAMP ATTORNEY July 28, 1964 J.A. BRINKMAN ETAL 3,142,539

METHOD FOR ARTIFICIAL SYNTHESIS OF DIAMONDS Filed July 1, 1960 5Sheets-Sheet 4 U l I I I 111/ Ill/I1 m H W M JOHN CHARL HER INVENTORS A.BRINKMAN ES J. MEEOHAN AN '4. DIEGKAMP ATTORNEY July 28, 1964 J. A.BRiNKMAN ETAL 3,142,539

METHOD FOR ARTIFICIAL SYNTHESIS OF DIAMONDS Filed July 1, 1960 5Sheets-Sheet 5 IN V EN TOR.

JOHN'A. BRINKMAN CHARLES J. MEEGHAN HERMAN M. DIEGKAMP MdM ATTORNEYUnited States Patent 3,142,53 METHOD FDR ARTIFICIAL SYNTI-ESIS 0FDIAMONDS John A. Brinlmian, Canoga Park, Charles J. Meechan, Reseda, andHerman M. Dieckamp, Canoga Park,

Califl, assignors to North American Aviation, Inc.

Filed July 1, 1960, Ser. No. 41,224 14 Claims. (Cl. 23-2091) Ourinvention relates to a method for artificially producing diamonds, andmore particularly to a method for producing large diamond crystals froma seed diamond. This application is a continuation in part of ourapplication S.N. 634,773, filed January 17, 1957, now abandoned, forMethod for Laboratory Diamond Production.

In nature, diamonds presumably were formed at high temperatures underextremely high pressures. Laboratory attempts to attain the necessaryhigh temperatures and pressures have utilized two general schemes. Thefirst involves rapid quenching of a saturated solution of carbon inmolten iron or other molten media, resulting in solidification at theouter surface first, the metal subsequently developing its own internalpressure. Due to the rapid cooling rates involved in such schemes, onlymicroscopic diamonds have been produced, since not enough time isallowed for sutficient diffusion of carbon atoms to produce reasonablylarge diamonds. The other scheme involves the use of extremely hightemperatures and pressures, of the order of 50,000 atmospheres, aboveabout 2200 K. Diamonds produced in this manner are quite small, and theproduction costs are not lower than the cost of natural diamonds, due tothe complex equipment required. Therefore, a method of diamondproduction which does not require extremely high pressures andtemperatures would be experimentally and economically desirable. Inaddition, if a continuous process of sufficient time duration could bedeveloped, the size limitations heretofore associated with artificialdiamond production could be eliminated.

Accordingly, an object of our invention is to provide an improved methodfor the artificial production of diamonds.

Another object is to provide such a method, which does not require useof extremely high temperatures and pressures.

Another object is to provide a method and apparatus for the productionof relatively large single diamond crystals from a small seed diamond ineither a batch or continuous process.

Still another object is to provide such a process for operation at aboutatmospheric pressure.

Other objects and advantages of our invention will become apparent fromthe following detailed description, taken together with the appendedclaims and the attached drawings.

In the drawings,

FIG. 1 is a longitudinal section of an apparatus suitable for theperformance of our invention;

FIG. 2 is a section through FIG. 1 along the lines 22;

FIG. 3 is an enlarged, partial section through lines 3-3 of FIG. 2;

FIG. 4 is a graph showing diamond growth rate under certain operatingconditions;

FIG. 5 is a perspective view of a modified version of the apparatus ofFIGS. 1-3;

FIG. 6 is a sectionalized view of another apparatus suitable for theperformance of our invention;

FIG. 7 is a sectionalized view of a different type of apparatus fromthose above which is also suitable for the performance of our invention.

In accordance with our present invention, we have provided a method forthe artificial production of diamonds which has a number of distinctadvantages over any previous method for the artificial production ofdiamonds. Extremely high temperatures and pressures are not necessary,and there is no known theoretical or practical limit to the size of thediamonds which may be obtained. Our process may be very suitablyconducted at the ambient atmospheric pressure, although there is norestriction to the use of higher pressures. Our method comprises broadlycontacting a seed diamond being maintained at a temperature of about12732073 K. with a flux of carbon atoms exceeding a critical minimumvalue. The critical condition for the carbon atom flux will be definedrigorously below. In general, the requirements which must be met fordiamond growth to occur by our method are:

(1) A seed diamond is heated to a temperature in the range of about1273-2073 K.;

(2) While the seed diamond is maintained in this temperature range, aflux of carbon atoms contacts the diamond surface;

(3) The flux of carbon atoms is sufiiciently small at the diamondsurface so that no appreciable graphite nucleation occurs, since in ourmethod we are growing the metastable structure of carbon, namely,diamond;

(4) The flux of carbon atoms exceeds a critical minimum value equal tothe rate at which carbon atoms are being removed from the diamondsurface.

These general requirements will be considered below for a particularsource of the carbon atom flux and for particular method used fortransporting the carbon atom flux from the carbon source to the surfaceof the seed diamond. There are two embodiments of our general method forartificial production of diamonds. In the first embodiment the source ofthe carbon atom flux is carbonaceous material dissolved in a moltenmedium, thus providing a solution of carbon atoms in the molten medium,and in the second embodiment carbonaceous material is heated to asufliciently high temperature to provide a vapor flux of carbon atoms.In the first embodiment, the carbon atoms are transported from thesource to the surface of the diamond seed by the molten medium. In thesecond embodiment, the carbon atoms are transported from the source tothe surface of the seed diamond via a vapor stream in a vacuum or aninert gas atmosphere.

MOLTEN MEDIUM PROCESS This embodiment comprises providing a solution ofcarbon in a molten medium, having a low carbon solubility, in a reactionapparatus upon which a temperature differential is imposed. Thistemperature differential arises as a result of one portion of thereaction apparatus being continuously maintained at a temperature Twhile another region of the apparatus is continuously maintained at ahigher temperature, T in a continuous process. This temperaturedilferential defined as may also arise as a result of cycling thetemperature of the entire reaction apparatus between T and T in abatch-type process.

In the continuous process, a seed diamond is positioned in a coolerregion of the apparatus, and the molten medium is circulated in theapparatus, its temperature changing from T to T and back to T again asit passes from the hotter to the cooler and back to the hotter region.The molten medium is saturated at T with carbon with respect toprecipitation of graphite in the hotter region of the apparatus andsupersaturated with carbon with respect to precipitation of diamond inthe cooler region at T thereby producing growth of the seed diamond as aresult of precipitation of carbon as diamond on the surface of the seeddiamond.

In the batch-type process, the molten medium is saturated with carbonwith respect to graphite precipitation While the reaction apparatus ismaintained at T The apparatus is then cooled to T and a seed diamond isinserted into the molten medium, which, at T is supersaturated withcarbon with respect to diamond precipitation, thereby producing growthof the seed diamond as a result of the precipitation of carbon asdiamond on the surface of the seed diamond. After a growth period, thediamond is removed from the molten medium, the apparatus is heated to Tand the cycle is repeated. The cycle may be repeated a plurality oftimes, depending on the desired size of the diamond crystal.

The essential condition for both the continuous and the batch-typeprocesses is thus the contacting of a seed diamond with a molten mediumin which the solubility limit of carbon is low, the molten medium beingsupersaturated with carbon with respect to diamond precipitation.

Precipitation of a solid from a liquid solution ordinarily occurs in acrystalline form of the solid. Graphite and diamond are the only solidcrystalline forms of carbon. Therefore, we need consider only these twostructures as possible forms of solid carbon which can be precipitated.Since the molar free energy of diamond exceeds that of graphite, thesolubility limit of carbon in any molten medium, when diamond is used asthe source material, exceeds that corresponding to the use of graphiteas the source material. Therefore, if a solution is saturated withcarbon with respect to precipitation of graphite, it is not yetsaturated with respect to precipitation of diamond. For the solution tobe also saturated with respect to precipitation of diamond, it must besupersaturated with respect to precipitation of graphite. The amount ofsuch supersaturation depends on the molar free energy difference, AG,between the diamond and graphite structures, which in turn depends onthe temperature of the solution. The required amount of supersaturationalso depends on the solubility limit of carbon on the molten medium,which may vary from one medium to another.

In this embodiment of our invention, the molten medium is saturated withcarbon, with respect to graphite precipitation, at T and as the moltenmedium is cooled to T at which temperature the seed diamond ismaintained, the molten medium becomes highly supersaturated with carbonwith respect to the precipitation of graphite, and also, if thetemperature differential, AT, exceeds a certain critical value, AT themolten medium is supersaturated with respect to the precipitation ofdiamond. The seed diamond provides a nucleus for such diamondprecipitation, which results in growth of the diamond. There is noappreciable graphite precipitation because the concentration of carbonin the molten metal is not sufiicient to permit graphite nucleation tooccur; thus, the precipitating carbon sees only one solid carbonstructure on which it may deposit, namely, the seed diamond.

To achieve positive diamond growth, the amount of carbon supersaturationwith respect to graphite precipitation which is required must exceed adefinite critical positive value. To achieve this minimum criticalsupersaturation of carbon with respect to precipitation of graphite at Tthe above-mentioned critical temperature differential AT is required.

The molten carrier medium is a metal or alloy which has a melting pointless than about 1773 K., and a boiling point greater than about 1473" K.The molten medium should further have a small but non-zero carbonsolubility limit at the operating temperatures, T and T which arebetween about 1273 K. and 3273 K. The

maximum operating temperature, T within such temperature range must notexceed a temperature at which the carbon solubility limit in the moltenmedium is greater than about 5% molar concentration. The low carbonsolubility limit in the molten medium is necessary so that graphiteprecipitation will be minimized or virtually eliminated. The termsmolten medium and low carbon solubility as used herein and in theappended claims are defined to have the above-indicated characteristics.

Satisfactory metals meeting the required criteria of melting and boilingpoints, and carbon solubility ranges, for use as the molten medium are,for example, copper, lead, aluminum, bismuth, gold, silver, antimony,tin, gallium, indium, and germanium. Such metals may be used eitherseparately or together, for instance copper-gold, silver-gold, andlead-tin alloys.

The derivation of the equations giving the critical supersaturation ofcarbon with respect to graphite precipitation required in the moltenmedium at T in order that diamond growth can be realized, and the methodfor obtaining from this critical supersaturation the criticaltemperature differential, AT are as follows:

The free energy of the solution (molten medium with carbon in solution)is given by the following expression:

G:XCGC+(1 XC)GM Here,

G (molar free energy of carbon in solution) molar free energy of solidcarbon),

G molar free energy of molten medium,

X :molar concentration of carbon in solution,

N =Avogadros number,

k Boltzmanns constant per atom,

T :absolute temperature.

The solubility limit is determined (to a good approximation) by settingoG OX Performing this operation, the following equation is obtained:

CL or.

Xnr.( 1 or.) X or.( 1 XDL From the preceding definitions of G and G itis seen that AG: (molar free energy of diamond) (molar free energy ofgraphite) G G =NIcT ln AG=G G =NICT l1] (3) In Equation 3, the quantitycan be approximated with good accuracy by unity, since a requirement ofour method is that X and X are small compared to unity. When thisapproximation is made, Equation 3 is solved, yielding:

The quantity, AG, in Equation 4 varies with temperature but is the samefor the various molten media. An expression giving its value as afunction of temperature is recorded in Journal of Research of theNational Bureau of Standards, vol. 21, p. 491 (1938). Using such anexpression, the value of the factor exp (AG/NkT) at each of a number oftemperatures is readily obtained.

In our method, the diamond seed is maintained in the temperature rangeof about 1273 K. to 2073 K. in order for diamond growth to occur sincebelow about 1273 K. the growth rate is negligible, and above about 2073K. the diamond seed spontaneously reverts to the graphite form.Throughout this temperature range, the factor exp (AG/NkT), in Equation4, is substantially equal to two. Therefore, Equation 4 can be rewrittenas:

for any of the previously mentioned molten media which are maintained atany temperature in the range 1273" K. 2073 K.

The physical significance of the foregoing derivation leading toEquation 5 is that the molten medium becomes saturated with carbon withrespect to diamond precipitation when the carbon content is twice thequantity required to saturate the medium with respect to graphiteprecipitation. When this concentration is exceeded in the vicinity ofthe seed diamond, the molten medium is then supersaturated with carbonwith respect to diamond precipitation, and positive diamond growth ratesare realized. To achieve this degree of supersaturation, the moltenmedium is first saturated with carbon with respect to graphiteprecipitation at a temperature in excess of T +AT The carbonconcentration achieved by this process is substantially retained uponcooling the medium to T and is sufiicient to provide, at thistemperature, the required supersaturation with respect to diamondprecipitation. In view of Equation 5, the critical temperaturedifferential, AT which must be achieved is equal to T T where T isdefined as that particular value of T at which X has twice the value ofX at the pre viously chosen T Values of X at temperatures in the presentrange of interest are recorded, for example, in Constitution of BinaryAlloys, 2nd edition, M. Hansen, Editor, McGraw-Hill Book Co., Inc., NewYork, 1958.

From the above criterion,

Metal T1(K.) T21(K c( Cu i 1, 7;; 1, 7; 100 1, 4 1, 2 250 Pb i 1, 723 1,873 150 Sb 1, 330 1, 540 210 1, 400 1, 600 200 The growth rate ofdiamond depends upon the amount by which the critical temperaturedifferential, AT is exceeded and also on the absolute temperature of thediamond seed. While diamond growth is realized for any positive amountor" supersaturation with respect to diamond precipitation in theproximity of the seed diamond, faster growth rates are achieved withfurther increase in supersaturation. Faster growth rates are alsoachieved by raising the temperature of the seed diamond. Since the seeddiamond is maintained at any temperature in the range of about 1273K.2()73 K., optimum growth rates are achieved by varying, within thistemperature range, either the amount by which AT exceeds AT.,, or thetemperature, T of the seed diamond, or by varying both.

The rate at which the diamond grows under any prescribed set ofoperating conditions (temperatures and medium) can be determined fromthe rate at which diamond dissolves in the medium when the carboncontent in said medium is substantially zero. Then, since the growthrate is substantially a linear function of carbon content, X and itsvalues are known at two values of carbon content, zero and X thestraight line showing the value of the growth rate as a function of Xcan be drawn. This is shown in FIG. 4 of the drawings.

As an example of a reaction apparatus for the continuous process whichachieves the conditions for diamond growth described above, we refer toFIG. 1. This system comprises a gas-tight enclosure 1 containing agraphite block 2 to hold the molten medium 3. The source of the carbonin the molten medium is the graphite container, since molten metalsdissolve carbon when in the form of graphite. The molten medium becomessaturated with carbon with respect to graphite precipitation in pool 3.Since the solubility limits for carbon in the medium under considerationare very low, the amount of graphite which is dissolved is very small,and therefore will not afiect the physical integrity of the system. Aninert gas atmosphere, such as helium or argon, is maintained inenclosure 1, the gas being introduced through a valved line 4. Themolten medium is introduced in block 2 by removing an end nut 5. Thethermal convection loop 6 is composed of two vertical arms 7 and 8,enlarged portion 9, and cross arm 10. The arms 7 and 8 are set in pool 3and are supported in the block 2 by other graphite blocks, which arescrewed into block 2. The loop 6 is composed of a high-melting-pointmetal such as molybdenum, tantalum, or tungsten, molybdenum beingpreferred. The metal selected must be resistant to corrosion by themolten medium. Enlarged portion 9 is hollowed out of a block 13 ofmolybdenum. The purpose of enlarged portion 9 is to provide a stagnantreservoir to prevent rapid flow of the molten medium (which mightinterfere with single crystal diamond growth), and the purpose of block13 is to radiate heat to provide a cooler leg for operation of the loopby thermal convection. Heat also escapes up a tube 16 which screws intoblock 13 and passes outside of container 1. Enclosing loop 6, down tothe level of blocks 11 and 12, is a sleeve 14 composed of, for example,one of the above metals or stainless steel and packed with thermalinsulating material 15 such as lampblack. Fluid flow is accomplished byinitially drawing the molten medium 3 into loop 6 by a vacuum pump whichreduces the pressure sufficiently to fill the loop, and the pressure isthere maintained by pressure regulator and ballast means. A seed diamond17 is positioned on a stand 18 held by a wire 19 in the enlarged portion9. The wire 19 passes out of portion 9 through a plug 20 at the entranceof tube 16. Vertical movement of wire 19 changes the position of stand18 in orifice 21; thus, stand 18 serves as a flow regulator. The stand18 and wire 19 are of one of the above metals, tantalum being preferredfor the stand because of its high density, and molybdenum beingpreferred for the wire. Additional insulating material 22, such aslampblack, fills enclosure 1 up to sleeve 4. Heater rods 23 pass throughcontainer block 2.

In FIG. 2, a section through 22 of FIG. 1, are seen a plurality of holes24 drilled through block 2, through which pass heater rods 23. As shownin FIG. 3, an enlarged section through 33 of FIG. 2, graphite sleeves 25are positioned in holes 24 to keep insulation 22 01f of heater rods 23.The heater rods do not touch graphite sleeves 25, to prevent shortcircuiting, and are spaced therefrom by insulating brick supports 26 onthe outside of container 1. Electrical connections 27 are made to rods23 outside of enclosure 1.

FIG. 5 shows essentially the same apparatus as that of FIGS. 1-3. Thesame reference numerals are used to identify common parts. The onlydifference of substance is that a molybdenum container 40 is positionedinside block 2. The purpose of this container 40 is to prevent possiblediffusion of the molten medium into the block. A thin graphite liner 42is in turn placed inside the container as the carbon source.

FIG. 6 shows another reaction apparatus suitable for the continuousprocess. This system comprises a gastight quartz enclosure 44 containinga graphite reservoir 46 which holds the molten medium 48. The source ofcarbon in the molten medium is the interior lining 50 of the graphitereservoir. Immersed in the molten medium is a molybdenum pot 52 whichcontains the molybdenum loop consisting of a horizontal arm 54 and avertical arm which communicate with molten medium 48 at ports 58 and 60,respectively. Inside the molybdenum pot 52 and surrounding the loop armsis lampblack insulation 64. A second vertical arm 62 communicating withhorizontal arm 54 is defined by containers 46 and 52. The diamond 66 isattached to a molybdenum or tantalum holder 68 and immersed in moltenmedium 4-8 in vertical arm 56. The molybdenum pot 52 is positioned on agraphite stand 70 which is perforated with holes 72. This allows themolten medium to flow entirely around the molybdenum pot. The graphitereservoir is heated by means of the induction coil 74, placed outside ofgas-tight container 44. Thermal insulation 76 is placed between thegas-tight container and graphite reservoir 46. A gas-cooled manifold 78(gas cooling lines not shown) is attached to the top of the vertical arm56 of the loop which allows for cooling this arm of the loop to thedesired temperature. The enclosure is filled with inert gas 80 such asargon or helium. Temperatures in hot and cold areas 62 and 56 may bemeasured by pyrometers through ports 82. Flow of the molten medium isaccomplished by heating the graphite reservoir holding the molten mediumby means of the induction coil, while simultaneously cooling thevertical arm of the molybdenum loop. The molten medium in the coolervertical arm will flow downward by means of thermal convection, into thebottom of the reservoir, up arm 62, through the horizontal arm of themolybdenum loop, and back into the vertical arm of the molybdenum loop.

Considering now operation of the above apparatus for the continuousprocess, using lead as an example of the molten medium, the lead becomessaturated with carbon with respect to graphite precipitation at atemperature of approximately l873 K. The solubility limit of carbon inlead at 1873 F. is about 2.1 atomic percent. At 1473 K., the solubilitylimit decreases to about 0.5 atomic percent. Thus, as the liquid leadflows into the region of the seed diamond, it becomes highlysupersaturated with carbon with respect to the precipitation of diamond.The insertion of a seed diamond, as shown in the figure, provides anucleus for such precipitation, which results in the growth of the seeddiamond. No appreciable amount of graphite nuclei will be present in thelead flowing into the right arm and the formation of such nuclei in thelead stream occurs at a negligibly small rate because of the lowconcentration of carbon (approximately 2 atomic percent) and the factthat a large number of carbon atoms must simultaneously diffuse togetherto form a graphite nucleus.

The flow rate of the molten medium in the apparatus is not critical andmay satisfactorily vary because the seed diamond is positioned in arelatively stagnant flow region to permit diamond crystal growth tooccur. The actual magnitude of flow rate is determined by the drivingforce (temperature differential, AT, across the loop), the geometry ofthe loop itself, and the physical characteristics (e.g., viscosity) ofthe particular medium used. The operating temperature, which varies withthe particular molten medium, will generally exceed 1273 K.

in the cold arm where the seed diamond is placed but will be less thanabout 3273 K. in the hot arm of the loop. When lead is the moltenmedium, the cold arm is preferably operated at approximately 1473 K. andthe hot arm at approximately l873 K.

It is apparent that since our method for artificial synthesis ofdiamonds can be performed with the continuous process in the loopsdescribed in the drawings, it may also be performed with a batch-typeprocess where desired. In the latter process, carbon may be dissolved inthe molten medium at an elevated temperature by lining the reactionvessel with graphite and providing the reaction vessel with a heatingmeans. The operation is then carried out at essentially atmosphericpressure as described previously in the definition of a batch-typeprocess. It should be noted that growth will continue for as long as thecritical condition is exceeded, this being determined by the degree ofsupersaturation and the temperature of the seed diamond, as explainedpreviously. Thus, there is no arbitrary time duration of each immersioncycle. After growth ceases, the diamond may be removed, the temperatureagain raised to dissolve additional carbon, and the cycle repeated asmany times as desired.

VAPOR TRANSPORT PROCESS In the vapor transport embodiment of ourinvention, the carbon atom flux is supplied by evaporating carbon atomsfrom the surface of a carbon source consisting of a hot carbonaceousmaterial such as graphite. The can bon flux originates at the hotgraphite surface and is transported in vapor form to the diamond surfacethrough vacuum or an inert gaseous medium such as argon or helium. Theterm inert environment" is intended to embrace either a vacuum or aninert gas atmosphere. In order to prevent graphite nucleation at thediamond surface, the carbon atom flux is maintained at a sufficientlylow level by regulating the temperature of the graphite source, which inturn regulates the rate of evaporation of carbon atoms. The graphitesource is maintained at a temperature in excess of a minimum value atwhich the carbon atom flux supplied to the diamond surface equals therate of evaporation of carbon atoms from the diamond surface. The carbonatoms reaching the diamond surface again see only the diamond structureon which to nucleate and therefore cause the seed diamond to grow. It isseen, therefore, that this embodiment of our method is equivalent inconcept and principle to the previously described operations performedin molten media. The specific critical requirements and the method forattaining the necessary conditions for diamond growth using the vaportransport adaptation of our method will now be considered.

The equilibrium vapor pressure of carbon over a solid carbon surface isgiven by an equation of the following form:

Pc= P FC/RT] Here, A is a constant depending on the units of pressuremeasurement and on the mass of the molecules which comprise the vapor.The quantity P is defined, in analogy with the definition given earlierfor G as F (molar free energy of carbon vapor)(molar free energy ofsolid carbon). Substituting first D, for diamond, and then G, forgraphite, into Equation 7 for C, and dividing the first of the resultingequations by the second, We obtain The quantity (P -F is equal to AG, aspreviously defined. Therefore, We can write PD=PG P in analogy withEquation 4, and since exp (AG/RT) is substantially equal to two in thetemperature range n 9 1273" K. to 2073 K., we can write, in analogy withEquation 5,

PD= PG The numerical form of Equation 7, for the case where graphite isthe solid surface, is

Then T the critical value of T for any previously chosen T is defined asbefore in Equation 6, except that graphite vapor pressures rather thansolubility limits are From Equations 11 and 12, T and therefore also thecritical minimum temperature dilferential, AT --T T can be obtained forthe case where graphite is used as a source of a carbon vapor atmospherein which a seed diamond grows.

From Equations 11 and 12, the relationship between T and T is found tobe 1 1 ln 2 T1 T2., 88,80O (14) From Equation 14, the value of T isdirectly calculable for any given value of T In our method, thetemperature of the diamond seed will always be in the range of aboutl273 K.-2073 K. Thus AT may be as low as about 10 K. (T =l273 K.) or ashigh as about 40 K. (T =2073 K.). It is to be noted here that althoughthe limiting value of T in the molten medium adaptation of our method isabout 3273 K., the limiting value of T for the vapor transportadaptation is about 4273 K. As stated above, however, the temperaturerange of the seed diamond is the same in every case, namely, 1273 K.2073K.

Positive growth rates of the diamond seed can only occur when thetemperature of the graphite source exceeds the value of T for anypreviously chosen T The complete analogy of this embodiment of ourinvention to that which makes use of a liquid medium as a carbon atomcarrier is obvious. The significant difference is that the carriermedium is now removed. The vapor pressures of the solid forms of carbon,rather than their solubility limits in the molten medium, are now beingdealt with. Since the free energy ditference between diamond andgraphite enters the equations in exactly the same manner in determiningthe ratio of vapor pressures of diamond and of graphite as it does indetermining their respective solubility limits, the same factor, too, isobtained for this ratio. In this case, therefore, it is possible andconvenient to simply consider the vacuum as the carrier medium and thesolubility limit of carbon in it to be just the equilibrium vaporpressure of carbon over a solid surface of the appropirate solid form ofcarbon.

In similar manner, the growth rates of diamond under specifiedconditions for this adaptation of our method are calculable from aknowledge of the dissolving rate into vacuum, that is, the rate ofvaporization of diamond in a system in which the carbon vapor iscontinually removed.

The rate of loss of carbon from a graphite surface at a temperature, T,is given in International Critical Tables of Numerical Data, Physics,Chemistry and T echnology, vol. V, p. 53, 1st Edition, McGraw-Hill BookCo., New York, 1929, as

m =eXp 32.6 1.25 In T) (15) loss of carbon from a diamond surface at atemperature T into a vacuum is substantially 5 a s 1n T1) Theequilibrium vapor pressure over a diamond surface, from Equations 10 and11 is p (T )=2 exp [(88,800/T )+25.5] (17) m T )=2 exp (32.6-

from a carbon atmosphere at a pressure, P, is equal to P PD( 1) M T 18When graphite is used as the source at a temperature, T the pressure, P,of carbon vapor in the vicinity of the seed diamond can be maintainedsubstantially equal to p (T Therefore, one can write for Equation 18 PD(T1) This is the equation for the straight line giving the diamond growthrate vs. the equilibrium vapor pressure of the graphite source,analogous to FIG. 4 for the molten media case. The quantities, m (T p (Tand p (T used in Equation 19, are given in Equations l6, l1, and 17,respectively.

In view of the foregoing exact equivalence of vapor and molten carriersin presenting the necessary flux of carbon atoms to the surface of theseed diamond, the term critical condition is defined to mean either X=2X at T or P=2p at T Thus, the critical condition is the establishmentof an environment in the vicinity of the seed diamond in Which either(1) the molar concentration of carbon in solution, X at the temperatureT of the seed diamond, is substantially equal to twice the solubilitylimit of graphite, X in the solution at T or (2) the pressure, P, ofcarbon vapor at T is substantially twice the value of the equilibriumvapor pressure of graphite, 1 at T The critical condition must beexceeded in order to achieve positive diamond growth rates.

An apparatus suitable for diamond growth using the vapor transportmethod is shown in section in FIG. 7. A graphite tube heater iselectrically heated by the attached water-cooled electrical leads 92.The seed diamond 94 is mounted inside graphite tube 90 on a molybdenumpedestal 96 having water cooling lines 98. The graphite tube issurrounded by a radiation shield 100. Pyrometer sight line ports 102 and104 are provided in tube heater 9t) and shield for measuring thetemperature of the tube and seed diamond. The seed diamond is heated byradiation from the interior walls of graphite heater 9% and cooled bywater-cooled molybdenum pedestal 96. The entire assembly is in a quartzenclosure 106 having a glass top 108 and positioned on a brass mountingplate 110. Gaskets 112 between the enclosure members give leaktightness, and a vacuum is drawn on the system through line 1114.Simultaneous adjustment of the cooling water flow rate and thetemperature of the graphite tube reactor allows the attainment of thedesired seed diamond temperature. The graphite tube serves both as aheat source for the seed diamond and also as the source of the carbonatom flux.

The following examples illustrate our invention in greater detail.

D= n(T1) Example 1 It is apparent from the preceding discussion thatwhen the carbon concentration, X in the molten medium in the vicinity ofthe diamond seed is twice the value of X a positive growth rate of thediamond seed is realized which is equal in magnitude to the dissolvingrate of diamond in said molten medium when X =0. Thus, the measurementof the dissolving rate of diamond in a molten medium where X =0, issubstantially a measurement of the growth rate of diamond in said moltenmedium when X =2X The following experiment is performed to measure thedissolving rate of diamond in lead when X is substantially equal tozero, and also to demonstrate that the dissolving rate of diamond inlead which was saturated with carbon with respect to diamondprecipitation is substantially zero. A diamond originally weighing0.0505 gram is X-rayed and placed in a container of pure lead (X atabout 1473 K. The weight of the diamond after two hours in the pure leadis reduced to 0.0484 gram and after three hours the weight is furtherreduced to 0.0418 gram. The weight is not altered, however, after anadditional two hours at 1473 K. in lead which had previously beensaturated with carbon using a graphite source at a temperature of about1723 K. After an additional two hours, however, at 1473 K. in pure lead,the weight is further reduced to 0.0399 gram. ray analysis of thediamond indicates that no detectable amount of diamond is transformed tothe graphite structure. Thus, while the dissolving rate of diamond inpure lead is quite appreciable at 1473 K., this rate can be reducedessentially to zero by saturating the lead with carbon by dissolvinggraphite at a temperature of about 1723 K. The dissolving rate ofdiamond in pure lead at 1473 K. is approximately 2.5 millimeters per day(linear dimensions). Thus the growth rate of diamond in lead at about1473 K. when the carbon content is equal to 2X is also about 2.5millimeters per day.

Example 2 The following example shows diamond growth by our methodemploying a batch-type process.

A reaction vessel made of molybdenum is lined with graphite and equippedwith heating means consisting of an induction coil. The reaction vesselis filled with lead and the temperature of the vessel and contentsmaintained within the range of 1843 K. to l873 K. for a period of 15minutes to insure saturation of the lead with carbon with respect tographite precipitation from the graphite lining acting as the carbonsource. The temperature of the reaction vessel and contents is thenlowered to substantially 1523 K. and four diamonds contained in aperforated molybdenum cage, weighing 46.13 milligrams, 50.77 milligrams,50.91 milligrams, and 48.08 milligrams, respectively, lowered into themolten lead which is kept at 1523 K., supersaturated with carbon withrespect to diamond precipitation. The diamonds are kept immersed in thelead-carbon solution for a period of minutes. The diamonds are thenwithdrawn, and the temperature of the reaction vessel and contents againraised to and maintained at substantially 1873 K. for a period of 15minutes and then lowered to substantially 1523 K. and the diamondsre-immersed in the lead-carbon solution. The cycle of saturating themolten lead with carbon from the graphite lining in the reaction vesselat the higher temperature of 1843 K. to 1873 K. and then cooling tosubstantially 1523 K. and inserting the diamonds for a period ofsubstantially 30 minutes is repeated five times until a total immersiontime for the diamonds of substantially 150 minutes is obtained. Thediamonds are next removed and boiled in nitric acid (3 parts ofconcentrated nitric diluted with 1 part of water by volume), so as toremove any lead adhering to the surface of the diamonds. The diamondsare again weighed and found to be 46.23 milligrams, 51.08 milligrams,51.12 milligrams and 48.45 milligrams, respectively. This representsweight increases of 0.1 milligram, 0.31 milligram, 0.20 milligram and0.37 milligram, respectively, for the four diamonds used in theexperiment. It is noted that the average weight increase for thediamonds is approximately 0.5% (0.2 milligram). Next the diamonds aresub- 12 jected to boiling aqua regia, washed with water, dried, and thensubjected to a temperature of substantially 1573" K. in vacuum for aperiod of 30 minutes. The diamonds are again weighed, and no change inweight detected.

The absence of change in weight upon washing in nitric acid and aquaregia indicates that the increase in weight is due to diamond growth andnot to contamination of the surface by the molten lead. The lack ofchange in weight upon subjecting the treated diamond to a temperature of1573 K. for 30 minutes supports this conclusion, since during thistreatment any lead on the diamond surface is removed by vaporization.

The electrical resistance of the deposited layer on the diamond ismeasured by placing the contacts of an ohmmeter across two faces, and aresistance of substantially 10,000 ohms observed. It is known that bort,a crystallized variety of diamond, is an electrical conductor as statedin the text, Diamond, a Descriptive Treatise, by I. R. Sutton, 1928Edition, published by D. Van Nostrand, Inc., New York. This establishesthat the diamond produced in this experiment is of the bort type.

Finally, X-ray patterns of the diamond containing the deposit arecompared with an X-ray pattern taken from a standard untreated diamond.No difference in the patterns is discernible, and no lines indicatingthe presence of any graphite structure are observable.

Example 3 The following example shows diamond growth by our method usingthe continuous process with lead as the molten medium. The apparatus ofFIG. 6 is employed with the loop constructed of molybdenum. A continuousflow path for the molten lead is established by thermal convection downthe vertical arm, through the bottom of the reservoir, up the side ofthe molybdenum pot, through the horizontal molybdenum arm and back tothe vertical arm. The vertical arm is cooled by a gascooled manifold andthe temperature of the lead in this arm is maintained at about 1520 K.The molten lead in the reservoir is maintained at about 1870 K. Thetemperatures of the hotter and colder regions of the molten lead aremeasured by means of optical pyrometry. The weight of a diamond ismeasured and is found to be 50.00 milligrams. This diamond is insertedin a molybdenum holder and this assembly is immersed in the molten leadin the vertical arm which is maintained at about 1520 K. The diamond isremoved after two hours, is etched in boiling nitric acid (3 partsconcentrated HNO to 1 part H O by volume) which removes the lead. Thediamond is heated in vacuum for 30 minutes to a temperature of about1570 K. which further cleanses its surface. The diamond is then weighedagain, the weight now being 50.25 milligrams, a weight increaseamounting to 0.25 milligram. X-ray examination of the diamond is nowperformed and it is found that only the diamond structure is detectable.A growth rate of the diamond surface of about 2.5 millimeters per day isachieved under these conditions.

Example 4 The following example shows diamond growth by our method usingthe continuous process of FIG. 6 with silver as the molten medium andtantalum as the loop structural material. Continuous flow of the moltensilver is then established by thermal convection as in Example 3. Thevertical arm is cooled by an attached gas-cooled manifold and thetemperature of the silver in this arm is maintained at about 1930" K.The molten silver in the reservoir is maintained at about 2080" K. Thetemperatures are measured by means of optical pyrometry. The weight of adiamond is measured and is found to be 40.00 milligrams. This diamond isinserted in a tantalum holder and immersed in the molten silver in thevertical loop arm which is maintained at about l930 K. The diamond isremoved after three hours, is etched in nitric acid (3 partsconcentrated HNO and 1 part H O by volume) which removes the silver. Thediamond is heated in vacuum for two hours at a temperature of about l570K. which further cleanses the diamond surface. The diamond is thenweighed again, the weight now being 40.20 milligrams, a Weight increaseamounting to 0.20 milligram. X-ray examination of the diamond is nowperformed and it is found that only the diamond structure is detectable.A growth rate of the diamond surface of about 1.7 millimeters per day ofinsertion in the loop is achieved under these conditions.

Example 5 The following example shows diamond growth by our method usingthe continuous process of FIG. 6 with antimony as the molten medium andmolybdenum as the loop structural material. Continuous flow of themolten antimony is established by thermal convection as in Example 3.The vertical arm is cooled by an attached gascooled manifold and thetemperature of the antimony in this arm is maintained at about l530 K,and the molten antimony in the reservoir is maintained at about 1800 K.The temperatures are measured by means of optical pyrometry. A diamondseed weighing 40.00 milligrams is inserted in a tantalum holder andimmersed in the molten antimony in the vertical loop arm, which ismaintained at about 1530" K. The diamond is removed after three hours,is etched in sulphuric acid (4 parts concentrated H 80 and 1 part H O byvolume) which removes the antimony. The diamond is heated in vacuum forone hour at a temperature of about l570 K. which further cleanses thediamond surface. The diamond is weighed again, the Weight now being40.30 milligrams, a weight increase of 0.30 milligram. X-ray examinationof the diamond is now performed and it is found that only the diamondstructure is detectable. A growth rate of the diamond surface of about2.2 millimeters per day is achieved under these conditions. Comparablegrowth rates are achieved using the other molten media disclosed above.

Example 6 The following example shows diamond growth by our method usingthe vapor transport process of FIG. 7 with graphite as the carbon sourcematerial. The interior walls of the center portion of the graphite tubeare maintained at about 3000 K. The seed diamond is heated by radiationfrom the graphite walls and is simultaneously cooled by conduction fromthe molybdenum stand on which it is supported. The equilibriumtemperature of the diamond is maintained at about 1600 K. Alltemperature measurements are made by means of optical pyrometry. Adiamond seed weighing 40.00 milligrams is heated in this manner to 1600K. for 12 hours. The diamond is removed and weighed again, the weightnow being 40.40 milligrams, an increase of 0.4 milligram. An Xrayexamination of the diamond reveals that only the diamond structure isdetectable. The rate of growth of the diamond surface under theseconditions is about 1.0 millimeter per day.

It should be appreciated that the above examples are illustrative ratherthan restrictive of our invention, which should be understood to belimited only as is indicated by the appended claims.

We claim:

1. A method for the artificialproduction of diamonds, which comprisescirculating a solution of carbon in molten lead under an inert gasatmosphere in a thermal convection loop having a cooler region and ahotter region containing a seed diamond positioned in the cooler regionof said loop, said molten metal being saturated with carbon with respectto precipitation of graphite in the hotter region of said loop andsupersaturated with carbon with respect to precipitation of bothgraphite and diamond in said cooler region, and wherein the minimumtemperature in the cooler region of said loop is approximately 1000 14C. and the maximum temperature in the hotter region of said loop isapproximately 3000 C., the minimum temperature differential across saidloop being approximately 250 0., thereby producing growth of saiddiamond as a result of the precipitation of carbon as diamond on thesurface of said seed diamond.

2. A method for the artificial production of diamonds, which comprisescirculating molten lead containing approximately 2 atomic percent carbonin solution under an inert gas atmosphere in a thermal convection loopcontainin a seed diamond positioned in the cooler region of said loop,the temperature in the hotter region of said loop being maintained atapproximately 1600 C. and the temperature in the cooler region of saidloop being maintained at approximately 1200" C., thereby producinggrowth of said diamond as a result of precipitation of carbon as diamondon the surface of said seed diamond.

3. A method for the artificial production of diamonds, which comprisescirculating a solution of carbon in molten lead under an inertatmosphere in a reaction apparatus having a first reaction zone and asecond reaction zone maintained at temperatures within the range of froml000 C. to about 3000 C., said first reaction zone containing a sourceof carbon for solution in said molten lead, said first reaction zonebeing maintained at a temperature sufficiently high to cause thesolution of said carbon in said molten lead, said second reaction zonehaving a seed diamond positioned therein, said second reaction zonebeing maintained at a temperature which is lower relative to thetemperature at which said first reaction zone is maintained to theextent that when the molten lead is saturated with carbon with respectto the temperature maintained in said first reaction zone issupersaturated with carbon with respect to graphite precipitation at thetemperature maintained in said second reaction zone to a degreesufiicient to exceed the solubility limit of diamond, circulating saidmolten lead through said first and second reaction zones thereby causingsolution of carbon in lead in said first zone and producing growth onsaid seed diamond as a result of the crystallization of carbon in theform of diamond on the surface of said seed diamond in said second zone.

4-. A method for the artificial production of diamonds, which comprisescirculating a solution of carbon in molten lead under an inertatmosphere in a thermal convection loop having a hotter region and acooler region, and containing a seed diamond positioned in the coolerregion of said loop, said molten metal being saturated with carbon withrespect to precipitation of graphite in the hotter region of said loopand supersaturated with carbon with respect to precipitation of graphitein said cooler region, the temperature in said hotter region being lessthan about 3000 C. and the temperature in said cooler region beinghigher than about 1000 C., and wherein the temperature differentialbetween said hotter region and said cooler region is of a magnitudewhich provides a supersaturation of carbon in said cooler region in anamount suiiicient to exceed the solubility limit of diamond, therebyproducing growth of said diamond as a result of the crystallization ofcarbon in the form of diamond on the surface of said seed diamond.

5. A method for the artificial production of diamonds which comprisescirculating a solution of carbon in a molten metal selected from thegroup consisting of lead,

copper, aluminum, bismuth, gold, silver, antimony, tin, gallium, indium,and germanium under an inert atmosphere in a reaction zone having ahotter region at a temperature less than about 3000 C. and a coolerregion at a temperature higher than about 1000 C., and containing a seeddiamond in said cooler region, wherein said molten metal is saturatedwith carbon with respect to graphite precipitation in said hotter regionand supersaturated with carbon with respect to graphite precipitation insaid cooler region, and wherein the temperature diiferential betweensaid hotter region and said cooler 15 region is of a magnitude whichprovides a supersaturation of carbon with respect to graphiteprecipitation in said cooler region in an amount sufficient to exceedthe solubility limit of diamond, thereby producing growth of said seeddiamond.

6. A method for the artificial production of diamonds which comprisescirculating a solution of carbon in a molten metal selected from thegroup consisting of lead, copper, aluminum, bismuth, gold, silver,antimony, tin, gallium, indium, and germanium under an inert atmospherein a thermal convection loop having a hotter region at a temperatureless than about 3000 C. and a cooler region at a temperature higher thanabout 1000 C., and containing a seed diamond in said cooler region,wherein said molten metal is saturated with carbon with respect tographite precipitation in said hotter region supersaturated with carbonwith respect to graphite precipitation in said cooler region, andwherein the temperature differential between said hotter region and saidcooler region is of a magnitude which provides a supersaturation ofcarbon with respect to graphite precipitation in said cooler region inan amount sufficieut to exceed the solubility limit of diamond, therebyproducing growth of said seed diamond.

7. A method for the artificial production of diamonds, which comprisescirculating a solution of carbon in molten lead under an inert gasatmosphere in a thermal convection loop having a cooler region and ahotter region containing a seed diamond positioned in the cooler regionof said loop, said molten metal being saturated with carbon with respectto precipitation of graphite in the hotter region of said loop andsupersaturated with carbon with respect to precipitation of bothgraphite and diamond in said cooler region, and wherein the minimumtemperature in the cooler region of said loop is approximately 1200 C.and the minimum temperature in the hotter region of said loop isapproximately 1600 C., the minimum tem perature diiferential across saidloop being approximately 250 0, thereby producing growth of said diamondas a result of the precipitation of carbon in the form of diamond on thesurface of said seed diamond.

8. A method for the artificial production of diamonds, comprisingproviding a solution of carbon in a molten metal having a low carbonsolubility, wherein said molten metal is supersaturated with carbon withrespect to diamond precipitation, contacting a seed diamond beingmaintained at a temperature of about 1273-2073 K. with saidsupersaturated carbon-molten metal solution, maintaining the pressure ofsaid solution throughout the period of contacting at about atmosphericpressure, thereby causing said carbon to crystallize out in the form ofdiamond on said seed diamond and causing said seed diamond to grow.

9. The method of claim 8 wherein said molten metal has a melting pointless than about 1773 K. and a boiling point greater than about 1473" K.

10. A method for the artificial production of diamonds comprisingproviding a solution of carbon in a molten medium having a low carbonsolubility, wherein said molten medium is supersaturated with carbonwith respect to diamond precipitation, said medium being selected fromat least one metal of the group consisting of lead, copper, aluminum,bismuth, gold, silver, antimony, tin, gallium, indium, and germanium,contacting a seed diamond being maintained at a temperature of about1273-2073 K. with said carbon-molten medium, maintaining the pressurethroughout the period of said contacting at about atmospheric pressure,thereby causing said carbon from said supersaturated solution tocrystallize out on said seed diamond in the form of diamond and causingsaid seed diamond to grow.

11. A method for the artificial production of diamonds, which comprisesproviding a solution of carbon in a molten metal having a low carbonsolubility, a melting pointless than about 1773 K. and a boiling pointgreater than about 1473 K., circulating said solution under an inert gasatmosphere in a thermal convection loop having a cooler region and ahotter region, a seed diamond being positioned in the cooler region ofsaid loop, said molten metal being saturated with carbon with respect toprecipitation of graphite in the hotter region of said loop andsupersaturated with carbon with respect to precipitation of bothgraphite and diamond in said cooler region, wherein the temperature ofsaid seed diamond is maintained at about l2732073 K., and wherein thetemperature differential between said hotter region and said coolerregion is of a magnitude which provides supersaturation of carbon withrespect to diamond precipitation in said cooler region, therebyproducing growth of said seed diamond.

12. A method for the artificial production of diamonds which comprisescirculating a solution of carbon in at least one molten metal selectedfrom the group consisting of lead, copper, aluminum, bismuth, gold,silver, antimony, tin, gallium, indium, and germanium under an inertatmosphere in a reaction zone having a hotter region and a coolerregion, and containing a seed diamond in said cooler region maintainedat a temperature of about 12732073 K., wherein said molten metal issaturated with carbon with respect to graphite precipitation in saidhotter region and supersaturated with carbon with respect to graphiteprecipitation in said cooler region, and wherein the temperaturedifferential between said hotter region and said cooler region is of amagnitude which provides a supersaturation of carbon with respect todiamond precipitation in said cooler region, thereby producing growth ofsaid seed diamond.

13. A method for the artificial production of diamonds which comprisescirculating a solution of carbon in at least one molten metal selectedfrom the group consisting of lead, copper, aluminum, bismuth, gold,silver, antimony, tin, gallium, indium, and germanium under an inertatmosphere in a thermal convection loop having a hotter region at atemperature less than about 3000 C. and a cooler region at a temperaturehigher than about 1000 C., and containing a seed diamond in said coolerregion being maintained at a temperature of about 1273-2073 K., whereinsaid molten metal is saturated with carbon with respect to graphiteprecipitation in said hotter region and supersaturated with carbon withrespect to graphite precipitation in said cooler region, and wherein thetemperature differential between said hotter region and said coolerregion is of a magnitude which provides a supersaturation of carbon withrespect to diamond precipitation in said cooler region, therebyproducing growth of said seed diamond.

14. A method for the artificial production of diamond which comprisescontacting a seed diamond being maintained at a temperature in the rangeof about 1273- 2073 K. with a solution of carbon in a molten metal in asystem wherein the critical condition for diamond growth is satisfied bythe equation X =2X at T where X is the molar concentration of carbon inthe molten metal, X is the solubility limit of graphite, and T is thetemperature within said temperature range at which the seed diamond ismaintained.

References Cited in the file of this patent UNITED STATES PATENTS1,637,291 Barnett July 26, 1927 2,675,303 Sobek Apr. 13, 1954 2,996,763Wentorf Aug. 22, 1961 3,030,188 Eversole Apr. 17, 1962 OTHER REFERENCESHershey: Trans. Kansas Acad. Sci, vol. 40, pages 109-111 (1937).

5. A METHOD FOR THE ARTIFICIAL PRODUCTION OF DIAMONDS WHICH COMPRISESCIRCULATING A SOLUTION OF CARBON IN A MOLTEN METAL SELECTED FROM THEGROUP CONSISTING OF LEAD, COPPER, ALUMINUM, BISMUTH, GOLD, SILVER,SNTIMONY, TIN, GALLIUM, INDIUM, AND GERMANIUM UNDER AN INERT ATMOSPHEREIN A REACTION ZONE HAVING A HOTTER REGION AT A TEMPERATURE LESS THANABOUT 3000*C. AND A COOLER REGION AT A TEMPERATURE HIGHER THAN ABOUT1000*C., AND CONTAINING A SEED DIAMOND IN SAID COOLER REGION, WHEREINSAID MOLTEN METAL IS SATURATED WITH CARBON WITH RESPECT TO GRAPHITEPRECIPITATION IN SAID HOTTER REGION AND SUPERSATURATED WITH CARBON WITHRESPECT TO GRAPHITE PRECIPITATION IN SAID COOLER REGION, AND WHEREIN THETEMPERATURE DIFFERENTIAL BETWEEN SAID HOTTER REGION AND SAID COOLERREGION IS OF A MAGNITUDE WHICH PROVIDES A SUPERSATURATION OF CARBON WITHRESPECT TO GRAPHITE PRECIPITATION IN SAID COLLER REGION IN AN AMOUNTSUFFICIENT TO EXCEED THE SOLUBILITY LIMIT OF DIAMOND, THEREBY PRODUCINGGROWTH OF OF SEED DIAMOND.